I've been using Gadgetbridge, installed via F-Droid, to interface with my Xiaomi Mi Band 4 for years now and can only recommend it. For my device, it's 100% feature-complete, it's VERY polished design- and UX-wise, and it comes without any ties to any vendor's data-siphoning cloud services. You can even set it up so that it works in parallel with your vendor-provided app, by not deleting any data from the device it fetches, if you're yet uncertain you actually want to use it as a replacement for your current app.
Free software at its very best, really!